 Another way to classify properties are to classify them as extensive or intensive and of course there is a somewhat related called specific property. So these are the three adjectives which can be associated with properties. First let us look at the extensive and intensive property. We consider a system, let us say this is our system, let us say system E and let us say that it has some property, let us call that property of this system X, could be pressure, it could be volume, it could be energy, some property, let us call that property X. Now let us imagine the partitioning of this system. That means imagine a surface separating the system into two parts, equal or unequal. Let us say this is part one and let us say this is part two. Part one and two totally make up a system A. Since this surface is properly defined, one by itself is a thermodynamic system, two by itself is another thermodynamic system. And system one, system two when combined together give us system A. This property X when measured for system A has the value X, but when measured for this part of the system, system one, let the value of the property be X1. And when it is measured for this part of the system, let the value of the property be X2. Now using X, X1 and X2, let us define extensive and intensive as follows. If X turns out to be X1 plus X2, then we say that X is an extensive property because it depends on the extent. If on the other hand, X turns out to be equal to X1 and equal to X2. If all three are equal, then we say that X is an intensive property. Illustration of an extensive property would be mass, volume, energy. Typical illustrations of intensive properties are temperature, pressure, say density. Let us now look at what is meant by a specific property. The specific property is defined as follows. If X is an extensive property of a system, then X by M, where M is the mass of the system is defined usually given the symbol small x or a lower case X and X is then known as the specific property. Property related to X. For example, a system has mass M, then V volume would be an extensive property. But V by M, which is specific volume, this will be a specific property. Similarly, we could take energy, enthalpy, entropy. These are extensive properties, but energy per unit mass or specific energy, enthalpy per unit mass or specific enthalpy and entropy per unit mass, which is specific entropy are all specific.